Now, blog posts can be substantive, and I think I've written plenty of wonky blog posts about tax policy in particular. But still. It takes some stones to call a blog post a "study." Another is an op-ed column. One is his own campaign's white paper! And it doesn't add up the math, it just makes assertions.

That leaves the famous Princeton study by Harvey Rosen. In his study, Rosen wrote that families making more than $100,000 would indeed pay $81 billion more in taxes (see pages 10-11). He's fuzzy about whether this means they'd pay a higher rate. He has lately protested that this is not what he meant.

He meant, instead, that these increased revenues would be the result of tremendous economic growth after Romney cuts taxes. You know--the kind of growth we experience after Bush cut taxes. Oh.

Another piece of Friday/weekend news was the letter from the staff of the Joint Committee on Taxation debunking Romney's plan. Now, this particular study did indeed make some assumptions (for example, that all the Bush rates would expire) that may not be the real-world case. Some of these assumptions worked against the Romney plan, but some of them actually worked in its favor. Dylan Matthews did a thorough job of discussing that. If you want all that wonkeralia, read him.

The bottom is that you just can't get to 20 percent rate reductions by eliminating loopholes. Can't. JCT says you can get to 4 percent rate reductions, one fifth of what Romney is calling for and saying is possible.

Meanwhile, for all the Republican touting of these six "studies," there's one study, Barro notes drolly, that the campaign has not released:

Finally, I would note one item that the Romney campaign does not cite in support of its tax plan: Any analysis actually prepared for the campaign in preparation for announcing the plan in February. You would expect that, in advance of announcing a tax plan, the campaign would commission an analysis to make sure that all of its planks can coexist. Releasing that analysis now would be to the campaign's advantage, helping them put down claims like mine that their math doesn't add up.

Why don't they release that analysis? My guess is because the analysis doesn't exist, and the 20 percent rate cut figure was plucked out of thin air for political reasons without regard to whether it was feasible.